1. Field of the Invention
The present invention relates generally to leads for use with cardiac stimulators, and more particularly to transvenous defibrillation leads and fixation mechanisms therefor.
2. Background Art
Various mechanisms have been proposed and used for fixing the distal end of a transvenous lead in place within a chamber of the heart, including tines, hooks, and helical screws. In some cases, the fixation member provides mechanical fixation only, whereas in other cases the fixation member also serves as a conductor to deliver electrical stimulus to cardiac tissue. Among endocardial leads and electrodes intended for use as shock electrodes in combination with implantable defibrillators, the more common approach has been to use electrodes having a relatively great length and surface area, and to secure the lead in contact with cardiac tissue only at the distal end thereof. In general, the shock electrode itself has not been secured in contact with cardiac tissue, which is believed to lower the defibrillation threshold and permit use of an electrode having a smaller surface area.